This will install just the bare-bones GCC compiler. It can safely be overwritten by XCode if you decide to reinstall it, or simple removed using the same command as that used for removing XCode.
reinstall RVM: http://beginrescueend.com/rvm/install/
Install the package manager “homebrew” from http://mxcl.github.com/homebrew/ and with it install libiconv.

$ brew install libiconv

This will install several files to homebrew’s home directory “/usr/local/cellar”
backup /usr/local/lib/libiconv.2.dylib, and copy /usr/local/cellar/libiconv/1.14/lib/libiconv.2.dylib into it’s place in /usr/local/lib

At this point you should have everything in place to install ruby 1.9.2 using RVM:

Im my experience (limited), changing CC in .profile does not change Lion’s (10.7.2) defaulting to i686-apple-darwin11-llvm-gcc-4.2. I wonder if this has anything to do with Apple’s own sym linking:
a partial: $ls -la /usr/bin | grep .*gcc.*: